Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

Waste water conditioning has nearly 150 years of history. During this
time, a method has developed that is considered to be state of the art.
While this method meets the requirements at hand, it is complicated and
expensive. The novel method breaks down the rigidly entrenched method and
simplifies it. In a plurality of stages, the only energy that is used is
gravity, which is readily available and free of cost. Thus, an
"alternative sewage treatment plant" has been developed, which has a
simpler method and is less expensive in terms of investment costs and
operating costs, at the same capacity, and requires only a fraction of
the previous required surface area. The most important characteristic of
the invention is that the novel method separates solids from waste water
immediately after entering the sewage treatment plant. Mechanically
purified water is much faster, easier and less expensive to purify. The
paths pursued for conditioning of the sludge are also new. The sludge is
regarded as an energy source or recyclable material, which should be
utilized accordingly. According to the invention, the prerequisite for
utilizing the sludge is also created by economically drying it to 95 to
98% dry substance.

Claims:

1. A method for conditioning municipal, industrial and agricultural waste
water, comprising: organic flocculant is admixed with the waste water,
solids are separated in a quick sedimentation tank by gravity,
mechanically purified water is chemically-biologically purified in a
bioreactor, the sludge collected in the quick sedimentation tank is
conducted into a pre-dewatering cylinder and a pre-thickening cylinder
and dewatered there by means of gravity, pre-thickened sludge is
re-pressed by means of a sludge press, the press cake is shaped into
pellets, the pellets are conveyed into a dryer through which the wet
pellets trickle as a result of gravity, wherein during this process the
pellets are permeated by warm drying air, containing flue gases from
industry or incineration, and dried to a high degree of dryness, and are
either loaded into containers to be transported away or into an
intermediate reservoir for further recycling, or the pellets are
pulverized so as to improve the dry substance of the sludge in a mixer
for pelletization, hot flue gases are cooled to the desired drying
temperature by admixing with outside air, drying air is drawn through a
dryer using a fan and pumped into a waste air conditioning system, where
dust is flushed out of the air, and the waste air is subjected to final
purification in a biofilter before it escapes via a chimney.

2. The method according to claim 1, wherein the flocculant is admixed to
a waste water stream via an injection pipe and a static mixer.

3. The method according to claim 1, wherein the flocculated waste water
is conducted into one or more quick sedimentation tanks and collected
sludge is suctioned from a cone using a hose pump, the operation of which
is controlled by a sludge level probe.

4. A method according to claim 1, wherein the waste water is introduced
in the bioreactor filled with carrier material in which bacteria have
been injected, and in which air is blown through in a counter flow
direction, including an option of backwashing.

5. A method according to claim 1, wherein a nitrate/phosphate elimination
system is installed in the outflowing water pipe.

6. A method according to claim 1, wherein the sludge that has been
thickened in the quick sedimentation tank is pre-dewatered by gravitation
in the pre-dewatering and the pre-thickening cylinders and is then
re-pressed on the sludge press.

7. The method according to claim 1, wherein the pressed-out sludge cake
drops into the mixer, where dry powder from the internal material that
has been conditioning in a pulverization system is admixed to the sludge
so as to increase the dry substance.

8. The method according to claim 1, wherein the mixture drops from the
mixture into a pelletizer that is provided with a cleaning system for the
perforated plate, where the mixture is shaped into pellets having various
diameters and lengths by means of extrusion.

9. The method according to claim 8, wherein the wet pellets are lifted
into dryers using suitable conveying means, where the pellets trickle
through the dryers and are subjected to hot air from flue gases or
another type of waste heat at a low temperature so as to dry the pellets,
wherein in several dryers the pellets are added by means of a
distribution belt having diverters and emptied by means of cellular wheel
sluices or slides onto a belt that can move in both directions.

10. A method according to claim 1, wherein the drying temperature of the
flue gases is controlled in an air admixing unit, where a motor
controlled by a thermostat admixes as much outside air as is needed to
reach the desired temperature via adjustable louvers or air valves.

11. A method according to claim 1, wherein a the fan, which draws the
drying air through the dryer, also pumps the air into a waste air
conditioning system, where dust is flushed out of the air using water and
the air is condensed out and subsequently biologically purified in the
bioreactor, wherein the waste heat that is released is utilized via heat
exchangers for water heating and the like.

12. A plant for carrying out the method according to claim 2, wherein an
injection pipe is provided for the metered addition of flocculant, the
injection pipe being installed in the waste water pipe by means of
flanges and comprising a flocculant distribution container having four
pipe nipples as outlets, which are connected to hoses having four pipe
nipples on the injection pipe, which are distributed over the
circumference and length of the pipe.

13. A plant for carrying out the method according to claim 3, wherein the
flocculated waste water is conducted in a round tank having a conical
outlet, an annular channel and an annular filter, where a mandrel
installed in the container creates two defined, opposing flows: a fast
downward flow and a slow upward flow wherein the water, which is
introduced at high speed, is decelerated in the container and rotated
upward because the water can drain only at the top into an annular
channel, the solids, having a higher specific weight than the water,
maintain the downward movement thereof for a longer period than the water
due to the inertia of the solids and collect in a cone of the tank in the
form of and the sludge is suctioned from the tank by a hose pump in
response to a signal from a sludge level probe.

14. A plant for carrying out the method according to claim 4 in a
bioreactor comprising an upright cylinder, which is filled with a
synthetic carrier material, the waste water is introduced at the top and
distributed over the filler material by means of a reaction wheel or
other distribution mechanism, the lower part of the tank is designed as a
basin, which is filled with water that drains off, the water level is
controlled by a spillway, connections are also provided for sludge
removal and for water for the backwashing of the carrier material, the
latter is also used as a water drain, valves are provided at the spillway
and air feed to prevent undesirable water drainage during backwashing, an
air cushion is formed over the water by keeping the carrier material at a
distance from the water surface using a stainless steel construction, a
fan blows air in the air cushion, and the air then uniformly permeates
the carrier material, for repair purposes, the tank is equipped with a
manhole, during operation, the tank is closed by a woven filter fabric,
the space over the reaction wheel is also filled with carrier material,
to which bacteria have been injected, and the waste air from the
bioreactor is thus purified.

15. A plant for carrying out the method according to claim 6 for
gravitational pre-dewatering of the sludge, comprising two stainless
steel cylinders which comprise two cylinders that are nested inside each
other, the inner cylinder comprises a filter medium, the outer cylinder
is used to collect the filtrates, a slow worm runs in the inner cylinder,
the sludge is introduced into the first cylinder from beneath and runs
through the cylinder from the bottom to the top, and through the second
cylinder from the top to the bottom, and is dewatered in between by
gravity, the filter cylinders are cleaned by means of a washing system,
and the pre-dewatered sludge leaves the second cylinder via a drain
mechanism.

16. A plant for carrying out the method according to claim 7, comprising
a powder conditioning system to enable the powder to be mixed with the
press cakes, comprising an intermediate reservoir for dry pellets,
combined with a mill, preferably a hammer mill having a powder container,
from where the powder is metered into the mixer using suitable means, and
the material is transported inside the plant by the effect of gravity.

17. A plant for carrying out the method according to claim 8, comprising
a pelletizer as the extruder made of steel, comprising a hopper, a full
and empty detection sensor, a loosening shaft, feed worm, working worm,
blade and perforated plate, the blade rotates in front of the perforated
plate and always keeps it clean, and the working worm, blade and
perforated plate can be reinforced.

18. A plant for carrying out the method according to claim 9, comprising
a diverting device on the filling belt, the belt has lateral upturns, the
upturn is interrupted at the filling opening of the dryer and designed as
a rotatable panel, which is fastened to the remaining upturn by hinges,
in response to a signal from the empty detection sensor of the dryer, the
panel opens 45.degree. and blocks the path of the pellets in the straight
direction. The pellets are diverted laterally into the dryer via a chute,
in response to a signal from the full detection sensor, the panel closes
again, releasing the path for filling the next dryer, the panel is opened
and closed by a pneumatic piston or electrically.

19. A plant for carrying out the method according to claim 9, comprising
a dryer made of galvanized steel, aluminum or stainless steel
construction having three pits, the center, large pit is the actual
dryer, the two lateral pits are used to introduce and distribute the
drying air or collect the waste air, the drying air is advantageously
introduced at approximately half the height of the dryer; the waste air
is discharged at the bottom on the intake side by means of a fan, the
dryer comprises modular units that are stacked on top of one another, in
this way, the capacity can also be controlled within a particular scope,
the modular units contain at least two, and sometimes four, rows of
ventilation channels, which are shifted by a half an axis on top of each
other, they connect the two lateral pits through the dryer shaft and are
distributed over the entire dryer pit, the air channels have a small
roof-like shape, which opens at the bottom, at the end faces, the
channels have openings on one side and are closed on the other side, the
channel rows located on top of one another have opposite polarities, the
air taken in through one channel row cannot exit on the other side, and
is forced to exit at the bottom and continue in the channel row above or
below, which has reverse polarity, the drying air is thus forced to
uniformly permeate the entire volume of pellets, the dryer is always
filled with pellets, which are replenished at the top and withdrawn at
the bottom at short intervals via cellular wheel sluices or slides, the
entire volume of pellets thus trickles through the dryer due to gravity
and is dried, the discharge device can be controlled, and in this way,
the residence time in the dryer, and thus the desired degree of dryness,
can be controlled, the dryer is seated on a base and comprises filling
and emptying funnels, full and empty detection sensors, a thermometer,
and control openings for cleaning the dryer, and the inlet side of the
air channels can be closed by slides, so that the dryer can be heated in
sections during filling.

20. A plant for carrying out the method according to claim 10, comprising
an air admixing unit for regulating the drying air, the flue gases
generally arrive at a higher temperature than the desired drying
temperature. In order to cool them to the desired temperature, outside
air is admixed to the flue gases, and this is done in a pipe-hose piece
in smaller plants, one side is installed in an air line, and the
projecting part is provided with an air valve, which is opened or closed
by a motor controlled by a thermostat, the thermostat is installed in the
outflowing air stream. In larger plants, a box is installed in the
cross-section of the air line, and louvers that can be adjusted by a
motor are located on both sides and operate according to the same
principle as the air valve.

21. A plant for carrying out the method according to claim 11, comprising
a vertical or horizontal component that has a square cross-section and is
made of reinforced concrete, the lower part is designed as a basin for
receiving the condensates, the waste air is introduced above the water
level, the chimney is located on the roof of the component, at a certain
height, nozzle fittings are provided, which have special spray heads that
spray downward, underneath a close-meshed stainless steel net is provided
to better disperse the water, a number of inclined water wiper blades
made of synthetic material are located above the nozzle fittings,
underneath a synthetic honeycomb design is provided, to which
microorganisms have been injected, as the biofilter for air purification,
the air, which is introduced horizontally, is rotated upward and
saturated with water in the counter flow direction to flush out the dust,
the dust collects in the basin as sludge, is periodically suctioned off
and disposed of, the flushing process cools the air and condenses it out,
the condensate collects in the basin and runs into an underground water
tank via a spillway, and from there, a pump--preferably a centrifugal
pump--suctions in the amount of water that is required for washing the
filter surfaces, the excess runs into the receiving waters via a spillway
or back to the sewage treatment plant inlet, the waste air scrubber
contains a plurality of inlet stages having a landing for the control
door and interior and exterior lighting, the water in the underground
container still contains a relatively large amount of heat, and this heat
is rendered usable by means of a heat pump or heat exchanger.

Description:

PRIOR ART

[0001] Given increased population densities and the associated pollution
of the environment, it is necessary to clarify municipal, industrial and
agricultural waste water (liquid manure). This is done by sewage
treatment plants, which have been being built for approximately 150 years
now, and in many instances have been adapted to new requirements, in
terms of the technology thereof. Today, technology exists that allows
waste water to be purified so that it can be discharged into public water
systems without posing a hazard.

[0002] The degree of pollution is characterized by various parameters. CSB
denotes the chemical oxygen consumption, which is to say the quantity of
oxygen that is required for degrading the chemical loads, BSB5 denotes
the same for biological pollution, the content of phosphates and nitrates
in mg/l, and the residual substances, likewise in mg/l, that can settle.
These limits vary from one country to another, but are relatively close
to each other everywhere.

[0003] In order to achieve the statutory limits, comprehensive sewage
treatment plants are being built, which degrade the aforementioned
pollutants in various process stages and use various technologies. A
classic sewage treatment plant thus comprises:

[0004] a coarse screen, where the coarsest pollutants such as rags,
condoms, fruit skins and the like can be separated. These pollutants are
pressed out and delivered to a disposal site or incinerated; then, a fine
screen follows, where additional, but still relatively large parts are
segregated.

[0005] a sand trap: Here, the flow of the water is slowed down, whereby
the heaviest inorganic matter, primarily sand, settles. This sand is
suctioned off by a continuously running suction mechanism and pumped into
a screen container, from where the sand is delivered to the disposal
site.

[0006] The sand is mixed with fecal matter, for which reason sand washing
systems are being built of late where the fecal matter is rinsed out.
This then allows the sand to be recycled in the building industry. The
disadvantage: the sludge produced in this way is several times more
expensive than pit sand or drift sand that is available in unlimited
quantities.

[0007] a mechanical sedimentation tank: Here, the flow of the water is
slowed down even further so as to separate matter that can settle. In
general, the water is expected to remain in the tank for six hours and
the settling rate is expected to be 1.00 m/hour. However, this settling
rate is not entirely sufficient. Together with the water, slowly settling
solid matter also finds its way into the biological stage.

[0008] a biological stage: This refers to large clarifying tanks, where
the organic matter still present in the waste water in dissolved form
(emulsion) is degraded (oxidized) using bacteria and the oxygen in the
air. Air can be supplied in a variety of ways. The presently conventional
form of air supply is to blow in air through the floor membranes. The air
thus bubbles through the entire volume of water and supplies the bacteria
with the necessary oxygen. Large compressors are continuously operated
day and night for this purpose.

[0009] a secondary clarifying tank: In the biological stage, the water is
swirled around, thus keeping many dirt particles, which primarily
comprise dead bacteria, suspended. These particles settle in the
secondary clarifying tank with the appropriate residence time before the
water is introduced into the receiving waters.

[0010] Formerly, waste water purification ended with the biological stage
and secondary clarifying tank. For several years now, we also have a
third purification stage available, this being phosphate-nitrate removal.
Because phosphates predominantly settle and end up in the sludge, the
nitrates must be degraded by means of nitrification-denitrification.

[0011] The more thorough the waste water purification process is, the
greater the residue that remains in the form of sludge. Organic sludge,
and in particular municipal sewage sludge, is a malodorous mass full of
bacteria and viruses, which is suctioned off the clarifying tanks in the
form of a thin slurry containing 0.5 to 1.5% dry substance (TS),
combined, thickened to approximately 7% TS, and putrefied in digestion
towers. This involves anaerobic (without oxygen) digestion, which lasts
20 to 30 days, depending on the method. The sludge must be constantly
heated to a temperature of 37° C. Methane gas forms in the
process, which is incinerated in co-generation plants, so as to generate
power. The heat of the waste gases is recirculated into the digestion
tower so as to heat the same to the required temperature of 37° C.
The heat that is generated generally suffices, but often, during the
winter months, the temperature requires boosting by way of primary energy
combustion (natural gas, heating oil).

[0012] The residual sludge remains in the digestion towers at 3.5 to 4.0%
TS, and this must be disposed of. Given the enormous quantities, this
sludge must be reduced using mechanical dewatering measures. The
centrifuge achieves approximately 22 to 26% TS, the belt press
approximately 24 to 30% TS, the chamber filter press approximately 28 to
35% TS, and the chamber membrane press up to 38% TS.

[0013] Thereafter, the dewatered sludge must be disposed of. Disposal as
fertilizer in agriculture, which was previously common, is decreasing for
a variety of reasons. Because organic sludge can no longer be used for
land fill, the only way to manage the waste is by incineration. Along
with this, the 62 to 78% of water must also be disposed. Because water,
as is known, does not burn, and the sludge having a high water content
cannot be incinerated by itself, large amounts of primary energy sources
(natural gas, heating oil) are required to dispose of this unpleasant
waste product on a daily basis.

[0014] The conventional sewage treatment plant also requires large surface
areas, which for a sewage treatment plant for a population equivalent of
100,000 can amount to 15,000 to 20,000 m2, depending on the
situation.

[0015] This complicated technology has high investment costs and operating
costs. These costs are apportioned among the households by sewage
authorities and paid together with the waste water charges.

[0016] This technology is well entrenched. Revolutionary changes to it are
no longer possible.

DESCRIPTION OF THE TECHNOLOGY OF THE ALTERNATIVE SEWAGE TREATMENT PLANT

[0017] The new technology goes back to the roots of the problem stated.
This problem is to economically purify waste water, so that the water can
be returned to the public water systems without harm, and the method
should be simple and affordable. The separated solids should not be
regarded as waste, but as energy sources or as recyclable materials, and
they should be treated and used accordingly.

[0018] The decisive factor for the new development was the realization
that the majority of the CSB and BSB5 pollutants can be found in the
solids. If these can be separated immediately upon entry of the waste
water in the sewage treatment plant, the remaining pollutants can be
degraded much more easily and quickly and at a lower cost.

[0019] To this end, it was also necessary to accelerate the settling rate
of the matter that can settle. For this purpose, the AQUEX RAPID quick
sedimentation tank was developed, whereby large amounts of waste water
can be mechanically clarified, quickly and thoroughly.

[0020] The existing conditioning of slurry also required critical
examination. The aim is to recycle the sludge; this cannot, however, be
used in the state in which it leaves the dewatering stage of the sewage
treatment plants. This requires dewatering at a high percentage level and
subsequent drying. Of course, the costs for the drying process must not
exceed the value of the end product. This means that drying using primary
energy forms is not possible in light of continuously rising energy
costs.

[0021] The digestion towers deserved special consideration. The sludge
that is withdrawn from the various clarifying tanks at 0.5 to 1.5% TS is
raw sludge. This raw sludge comprises approximately 75% organic material.
Approximately 35% of this is metabolized in the digestion tower, which is
to say converted into methane gas. This corresponds to 46.7% of the total
energy content.

[0022] The gas is incinerated in co-generation plants, thus generating
power. At a 90% incinerator efficiency, 42% of the energy remains, from
which approximately 35% power, which is to say 14.7% of the total energy
content is generated.

[0023] The exhaust heat is used to heat the digestion tower, which is to
say for internal purposes. The digestion tower, which is associated with
very high construction costs, thus provides an energy output of only
14.7% of the total energy content. This is extraordinarily low,
considering that the residual sludge from the digestion tower still has
to be dewatered and disposed of (destroyed) at an energy content that is
still high.

[0024] With drying and incineration of the sludge, the total energy
content can be thermally recycled and 29.17% power, which is
approximately double the amount, can be generated. The residual heat is
used to dry the sludge to 95 to 98% TS. The waste heat that develops
during the subsequent waste air conditioning is still high and can be
used to generate hot water, together with the many recycling options that
are associated therewith. Only the ashes have to be disposed of, but
these ashes can also be utilized in a variety of ways.

[0025] All these are compelling arguments to dispense with the expensive
digestion tower, which dissipates energy.

[0026] The technical changes are intended to radically lower the
investment costs and operating costs.

[0027] These are the objectives of the alternative sewage treatment plant.

[0028] The technology of the alternative sewage treatment plant comprises
two parts:

[0029] waste water conditioning and sludge treatment, with the objective
of obtaining a recyclable material as the end product for the subsequent
thermal or material recycling process.

[0030] Waste Water Conditioning (FIG. 1)

[0031] The waste water passes through the coarse screen and strainer (0)
where the coarsest solids are separated. These are treated as in
conventional sewage treatment plants.

[0032] The waste water is suctioned from an intermediate reservoir (1)
using a suction pump (2) and pumped into the AQUEX RAPID quick
sedimentation tank (5). However, prior to that, organic flocculant is
added to the waste water stream from a flocculant conditioning plant (7)
using a flocculant metering pump (8). The addition is preferably carried
out via an injection pipe (3) so as to uniformly distribute the
flocculant in the waste water. Optionally, it is also possible to add
flocculant in the suction pump. The waste water is provided with the
intermediate residence time required for flocculation in a static mixer
(4).

[0033] The solids are separated from the liquid in the quick sedimentation
tank. The quick sedimentation tank is a device that is described in
patent application DE 44 26 052 A1. The disclosure of this German patent
application is hereby expressly referenced and incorporated in the
present application. The essential idea of this quick sedimentation tank
is that two defined, opposing flows are artificially produced in a
circular tank having a conical outlet: a fast downward flow and a slow
upward flow. The flocculated waste water, which is conducted into the
tank at high speed, is decelerated in the tank and rotated slowly upward
because the water can drain only at the top, into an annular channel.
However, the solids, having a higher specific weight than the water,
maintain the downward movement thereof for a longer period than the
water, due to inertia of the solids, and collect in the cone of the tank
as sludge. From here, the sludge is suctioned off periodically using a
hose pump (6).

[0034] A sand trap, a sand washing system and a mechanical sedimentation
tank are deliberately omitted. The sand remains in the sludge. This has
several advantages. The cost of the sand trap and sand washing system is
saved, and the sand causes drainage in the sludge, resulting in improved
dewatering results. The sand can be found in the ashes following the
incineration of the sludge, making them recyclable in a variety of ways.

[0035] The mechanically purified waste water is suctioned in from an
intermediate reservoir (9) by means of metering pumps (10) and is pumped
into a bioreactor (11). The bioreactor is an upright cylinder, which is
filled with synthetic carrier material for bacteria. The introduction of
the waste water and the distribution should advantageously be done so
that a layer of filler material measuring 30 to 40 cm in thickness
remains above the point of introduction. The air exiting the bioreactor
is thus also purified and no gases can escape. Bacteria are injected into
the filler material. Optionally, it is possible to admix enzymes to the
waste water so as to expedite the multiplication of the bacteria. Excess
air is blown through from beneath as a counter flow, using a fan (12), so
as to supply the bacteria with sufficient oxygen. The blowing is done
such that an air cushion is formed at the bottom, in which the pressure
is uniform. The entire reservoir cross-section is thus supplied uniformly
with air.

[0036] The remaining CSB and BSB5 pollutants are degraded in the
bioreactor so that the water can be conducted into the receiving waters.
It shall be expressly pointed out that this is only possible because the
CSB and BSB5 pollutants have been significantly lowered by separating the
solids in the quick sedimentation tank. Large-scale tests have shown that
the CSB and BSB5 pollutants can be reduced between 55 and 58% in
municipal waste water, and as much as 95% in liquid pig manure, by
separating the solids.

[0037] Optionally, it is of course also possible to biologically purify
the mechanically purified water in the conventional manner using a
biological tank.

[0038] The nitrates are also partially degraded in the bioreactor.
Depending on the waste water, this degradation may suffice to meet the
approved limits. Should this not be the case, a small denitrification
system can optionally be connected downstream of the bioreactors. The
phosphates do not cause any problems and remain in the sludge.

[0039] Sludge Conditioning

[0040] The sludge, which also contains the sand, collects in the cone of
the quick sedimentation tank. It is already flocculated and can thus be
directly dewatered, without further treatment. It is necessary that the
slurry be gently moved into the dewatering units without destroying the
flocculation structure that has formed. For this reason, a hose pump is
used for this purpose.

[0041] The sludge is suctioned off periodically. The work of the hose pump
is regulated by a sludge level probe. This process also ensures that the
sludge does not become too thick in the cone of the tank, which can
negatively influence suctioning. Large-scale tests have shown that the
degree of thickening in the cone can reach 25 to 30% TS, depending on the
type of waste water.

[0042] The sludge that is suctioned off is raw sludge and, in this state,
still contains all the organic components, and thus the full energy
content. This energy content should be retained fully until this is
thermally recycled or used as fertilizer.

[0043] When conditioning sludge in the alternative sewage treatment plant,
the biological stage and digestion tower, which dissipate energy, are
entirely dispensed with.

[0044] The sand remains in the sludge and can be found in the ashes
following the incineration. The sand causes drainage in the sludge and
thus advantageously impacts the dewatering process.

[0045] The sludge that has been suctioned from the quick sedimentation
tank is pumped into a pre-dewatering cylinder where it is pre-dewatered
by gravity. The TS that can be achieved is approximately 25 to 28% for
raw municipal sludge.

[0046] From the pre-dewatering cylinder, the pre-dewatered sludge slides
into the pre-thickening cylinder, where it is further dewatered, also by
gravity. The degree of dewatering can amount to 30 to 35% for raw
municipal sludge.

[0047] The pre-dewatered sludge drops onto a belt press and is pressed
further to 40 to 44% TS. Given the thorough pre-dewatering, a smaller
press is also sufficient. The sludge can be pressed at a higher pressure
than customary, which is one of the reasons why the press achieves an
unusually high degree of dryness.

[0048] In addition, the sludge should be dried. In order to be able to
conduct drying economically, the sludge must be pelletized. In the
alternative sewage treatment plant, this is done by extrusion. For this
purpose, an extruder is used, in which the perforated plate is
automatically and continuously cleaned, so as to prevent clogging of the
dies.

[0049] Drying is carried out in a trickle drying shaft. The wet pellets
are added at the top, and the dry pellets are removed at the bottom,
using appropriate opening elements. The material trickles through the
dryer due to gravity and is subjected to hot air from horizontal drying
channels.

[0050] The dry pellets typically drop, at approximately 95 to 98% TS, onto
a conveyor belt and are loaded into containers or intermediate reservoirs
for recycling (for example incineration and power generation). The degree
of dryness, however, can be adjusted randomly if desired by regulating
the emptying step.

[0051] The drying air normally comprises flue gases from industry or from
the thermal recycling of the sludge. Drying is carried out at low
temperatures so as to prevent increased vapor formation. Flue gases
having higher temperatures are cooled to the desired temperature in a
bypass controlled by a thermostat by supplying outside air. The
pelletization and the trickle shaft dryer prevents undesirable dust
formation, which can result in dust explosions, with organic sludge.
Optionally, arbitrary heat sources can be utilized by means of heat
exchangers.

[0052] By diluting the flue gases, the temperature of the outside air is
also used for drying, whereby drying energy is saved.

[0053] A fan draws the drying air through the dryer and pumps it to the
waste air conditioning station. This creates a negative pressure in the
dryer which prevents gases from escaping from the dryer.

[0054] The waste air conditioning process comprises a waste air scrubbing
step using a biofilter, where the air is purified mechanically and
biologically before it leaves the system via a chimney.

[0055] During the waste air conditioning process, waste heat is generated
which can be used to produce hot water. Hot water can be used in a wide
variety of ways (for example, for heating buildings, greenhouses,
stables, and the like).

[0056] The entire energy of the sludge is thus used 100% three times in a
row: for generating power, for drying, and for internal operational
purposes.

[0057] Economic Efficiency

[0058] An alternative sewage treatment plant can be constructed at
approximately 30 to 50% of the existing investment costs at the same
efficiency. The operating costs are reduced to the same degree. The size
of the land parcel required by the alternative sewage treatment plant is
only approximately 5 to 10% of the usual surface area.

[0059] Given the economic efficiency of the alternative sewage treatment
plant, it in particularly suitable for construction in developing and
emerging countries. However, existing sewage treatment plants can also be
operated with some of the new technology. For example, the burden on
overloaded sewage treatment plants can be relieved by providing one or
more quick sedimentation tanks, without having to build a new plant.

[0060] The conditioning of the sludge using pelletization, drying,
incineration and power generation can also be employed effectively in
existing sewage treatment plants.

[0061] By using the quick sedimentation tank and bioreactor, the problem
of conditioning waste water in thinly populated areas can be solved
economically, because the construction of expensive collectors can be
avoided.